Enhanced classification for power over ethernet

ABSTRACT

A method of classification of power requirements in a power over Ethernet system, the method comprising: providing a first classification voltage for a first classification cycle time, the provided first classification voltage being within a classification voltage range defined by a lower classification voltage limit and upper classification voltage limit; measuring a first current flow responsive to the provided first classification voltage; subsequent to the first classification cycle time, providing a voltage outside of the classification voltage range for a classification indexing time; subsequent to the classification indexing time, providing a second classification voltage for a second classification cycle time, the provided second classification voltage being within the classification voltage range; measuring a second current flow responsive to the provided second classification voltage; determining a classification responsive to the measured first current flow and the measured second current flow; and allocating power responsive to the determined classification.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/735,253 filed Nov. 10, 2005, the contents ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the field of power over Ethernet andmore particularly to classification of power requirements for high powerdevices.

The growth of local and wide area networks based on Ethernet technologyhas been an important driver for cabling offices and homes withstructured cabling systems having multiple twisted wire pairs. Theubiquitous local area network, and the equipment which operates thereon,has led to a situation where there is often a need to attach a networkoperated device for which power is to be advantageously supplied by thenetwork over the network wiring. Supplying power over the network wiringhas many advantages including, but not limited to: reduced cost ofinstallation; centralized power and power back-up; and centralizedsecurity and management.

Several patents addressed to this issue exist including: U.S. Pat. No.6,473,608 issued to Lehr et al., whose contents are incorporated hereinby reference and U.S. Pat. No. 6,643,566 issued to Lehr et al., whosecontents are incorporated herein by reference. Furthermore a standardaddressed to the issue of powering remote devices over an Ethernet basednetwork has been published as IEEE 802.3af-2003, whose contents areincorporated herein by reference, and is referred to hereinafter as the“af” standard. A device receiving power over the network wiring isreferred to as a powered device (PD) and the powering equipmentdelivering power into the network wiring for use by the PD is referredto as a power sourcing equipment (PSE).

The “af” standard limits the amount of power available to a powereddevice to 12.95 watts, and devices demanding power in excess of the12.95 watt power limit are not supported. In order to meet growing powerdemands, in particular demands for PDs drawing in excess of 12.95 watts,a task force entitled “IEEE 802.3at DTE Power Enhancements Task Force”has been formed, which is in the process of producing a higher powerstandard, hereinafter the “at” standard. While the task force has notyet finalized its recommendations, it appears that the proposed “at”standard will specify a higher current limit than the “af” standard, andthat PSEs meeting the “at” standard are to support PDs meeting the “af”standard. Devices according to the “af” standard are hereinafteralternatively denoted low power device and devices according to theproposed “at” standard, or proposed standard, are hereinafteralternatively denoted high power devices. It is to be noted that highpower devices may draw less power than an “af” device, however operationis according to the proposed “at” standard for high power devices.

The “at” standard is expected to exhibit certain interoperabilityconditions regards “af” and “at” equipment. For example, in the eventthat an “at” PD is connected to an “af” PSE, it is an objective that the“at” PD will notify the user that the power sourcing equipment is of the“af” variety, and thus unable to support full powering under the “at”standards. Similarly, an “at” PSE having an “af” PD attached thereto isexpected to identify the PD as being an “af” PD, and further supportpowering in accordance with the “af” standard. Preferably, such mutualidentification is unambiguous, and operates consistently.

In order to improve overall system power and load management, the “af”standard provides for PD classification to one of 4 potential classes.Each class exhibits a range of maximum power drawn by the PD.Unfortunately, of the 4 potential classes, class 4 is reserved forfuture use, and class 0 is defined as a default class in which no powerrequirement information is supplied by the PD. Thus, effectively only 3power requirement classes are provided. The “at” standard is expected toprovide additional classes however, as indicated, above anyclassification method must provide for cross compatibility and avoidambiguity.

What is needed, and not supplied by the prior art, is a method ofclassification for high powered devices which in unambiguous, iscompatible with prior art classification under the “af” standard andconfirms to both the PD and the PSE the characteristics of the connecteddevice.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toovercome the disadvantages of prior art. This is provided in the presentinvention by a classification scheme exhibiting a plurality ofclassification cycles within the classification voltage range, with thePSE voltage being removed from the classification voltage range betweencycles. Preferably, the PD provides a current signature prior to the endof the plurality of cycles by exhibiting a first current outputassociated with a first class and a second current output associatedwith a second class. Further preferably the current signature ispreceded by a current level not associated with a classificationcurrent. Preferably the first and second classes are numericallyadjacent classes. Further preferably the first and second classes areconsecutively output with no substantial intervening time. Preferablythe PSE outputs a voltage signature indicative that it is an “at” PSE,the output voltage signature comprising lowering the output voltage atthe end of the plurality of cycles to be less than the classificationvoltage range.

The invention provides for a method of classification of powerrequirements in a power over Ethernet system, the method comprising:providing a first classification voltage for a first classificationcycle time, the provided first classification voltage being within aclassification voltage range defined by a lower classification voltagelimit and upper classification voltage limit; measuring a first currentflow responsive to the provided first classification voltage; subsequentto the first classification cycle time, providing a voltage outside ofthe classification voltage range for a classification indexing time;subsequent to the classification indexing time, providing a secondclassification voltage for a second classification cycle time, theprovided second classification voltage being within the classificationvoltage range; measuring a second current flow responsive to theprovided second classification voltage; and determining a classificationresponsive to the measured first current flow and the measured secondcurrent flow.

In one embodiment the method further comprises allocating powerresponsive to the determined classification. In another embodiment themethod further comprises subsequent to the second predeterminedclassification cycle time, providing a signature voltage for a voltagesignature time, the signature voltage being below the classificationvoltage range. In another embodiment the method yet further comprisessubsequent to the predetermined voltage signature time, providing anoperating voltage. In another the method yet further comprises in theevent that the signature voltage is not detected, identifying a powersourcing equipment associated with the classification voltage as a lowpower source.

In one embodiment the first current flow and the second current flow areof different values. In one further embodiment the differening value ofthe current flow is responsive to the voltage outside of theclassification voltage range for the classification indexing time.

In one embodiment the method further comprises responsive to theprovided second classification voltage: providing the second currentflow at a first value for a first time period, the first value exceedinga default classification value limit; subsequent to the first timeperiod, reducing the second current flow to a second value for a secondtime period, the second value being less than the default classificationvalue limit; subsequent to the second time period, increasing the secondcurrent flow to a third value for a third time period, the third valueexceeding the default classification value limit; subsequent to thethird time period, changing the second current flow to a fourth valuefor a fourth time period, the fourth value exceeding the defaultclassification value limit and being different than the third value, thesecond, third and fourth values for the respective first, second andthird time periods defining a current signature. In one embodiment themethod yet further comprises detecting the current signature, andidentifying a powered device associated with the current signature as ahigh power device. In one further embodiment the default classificationvalue limit is 5 mA.

In one embodiment the lower classification voltage limit is 15.5 volts.In another embodiment the upper classification voltage limit is 20.5volts.

The invention independently provides for a power over Ethernet systemcomprising: a power sourcing equipment, comprising a classificationfunctionality operable to: provide a first classification voltage for afirst classification cycle time, the provided first classificationvoltage being within a classification voltage range defined by a lowerclassification voltage limit and upper classification voltage limit;measure a first current flow responsive to the provided firstclassification voltage; subsequent to the first classification cycletime, provide a voltage outside of the classification voltage range fora classification indexing time; subsequent to the classificationindexing time, provide a second classification voltage for a secondclassification cycle time, the provided second classification voltagebeing within the classification voltage range; measure a second currentflow responsive to the provided second classification voltage; anddetermine a classification responsive to the measured first current flowand the measured second current flow.

In one embodiment the power over Ethernet system further comprises apowered device connected to the power sourcing equipment over acommunication cabling, wherein the power sourcing equipment is furtheroperable to allocate a predetermined amount of power to the powereddevice responsive to the determined classification. In anotherembodiment the classification functionality is further operative to:provide a signature voltage for a voltage signature time subsequent tothe second predetermined classification cycle time, the signaturevoltage being below the classification voltage range.

In one embodiment the power sourcing equipment is operable subsequent tothe predetermined voltage signature time to provide an operating voltageto the powered device. In another embodiment the powered device isoperable in the event that the signature voltage is not detected toidentify the power sourcing equipment as a low power source.

In one embodiment the powered device is operable responsive to thevoltage outside of the classification voltage range for theclassification indexing time to set the second current flow to adifferent value from the first current flow. In another embodiment thepowered device comprises a control circuitry and a current sourceresponsive to the control circuitry of the powered device, and whereinthe control circuitry of the powered device is operable responsive tothe provided second classification voltage to: provide the secondcurrent flow from the current source at a first value for a first timeperiod, the first value exceeding a default classification value limit;subsequent to the first time period, reduce the second current flow fromthe current source to a second value for a second time period, thesecond value being less than the default classification value limit;subsequent to the second time period, increase the second current flowfrom the current source to a third value for a third time period, thethird value exceeding the default classification value limit; andsubsequent to the third time period, change the second current flow formthe current source to a fourth value for a fourth time period, thefourth value exceeding the default classification value limit and beingdifferent than the third value, the second, third and fourth values forthe respective first, second and third time periods defining a currentsignature. In one further embodiment the classification functionality iffurther operable to: detect the current signature; and identify apowered device associated with the current signature as a high powerdevice. In one embodiment the default classification value limit is 5mA.

In one embodiment the lower classification voltage limit is 15.5 volts.In another embodiment the upper classification voltage limit is 20.5volts.

The invention independently provides for a power over Ethernet systemcomprising: a powered device; a power sourcing equipment connected tothe powered device over a communication cabling, the power sourcingequipment comprising a classification functionality and a current sensorand operable to: provide a first classification voltage for a firstclassification cycle time, the provided first classification voltagebeing within a classification voltage range defined by a lowerclassification voltage limit and upper classification voltage limit;measure, via the current sensor, a first current flow provided by thepowered device responsive to the provided first classification voltage;subsequent to the first classification cycle time, provide a voltageoutside of the classification voltage range for a classificationindexing time; subsequent to the classification indexing time, provide asecond classification voltage for a second classification cycle time,the provided second classification voltage being within theclassification voltage range; measure, via the current sensor, a secondcurrent flow provided by the powered device responsive to the providedsecond classification voltage and the voltage outside of theclassification voltage range; determine a classification responsive tothe measured first current flow and the measured second current flow;and allocate power to the powered device responsive to the determinedclassification.

In one embodiment the powered device comprises at least one currentsource, the first and second current flows being provided by the powereddevice by the at least one current source. In another embodiment thepowered device comprises a variable current source, the first and secondcurrent flows being provided by the powered device by the variablecurrent source.

In one embodiment the powered device comprises a voltage sensor, acontrol circuitry in communication with the voltage sensor, and at leastone current source responsive to the control circuitry, the controlcircuitry being operable to: detect, via the voltage sensor, the firstclassification voltage; provide, via the at least one current source,the first current flow; detect, via the voltage sensor, the voltageoutside of the classification voltage range and the subsequent secondclassification voltage; and provide, via the at least one currentsource, the second current flow. In another embodiment the at least onecurrent source comprises a variable current source.

In one embodiment the control circuitry is further operable to provide,via the at least one current source, subsequent to the provided secondcurrent flow and responsive to the second classification voltage, athird current flow exhibiting a value less than a default classificationvalue limit, and a fourth current flow subsequent to the third currentflow, the fourth current flow exhibiting a value exceeding the defaultclassification value limit. In one further embodiment the controlcircuitry is further operable to provide, via the at least one currentsource, subsequent to the provided fourth current flow and responsive tothe second classification voltage to provide fifth current flowexhibiting a value exceeding the default classification value limit anda value different than the fourth current flow.

Independently, the invention provides for a powered device for a powerover Ethernet system comprising: a control circuitry; a voltage sensorin communication with the control circuitry; and at least one currentsource responsive to the control circuitry, the control circuitry beingoperative to: detect, via the voltage sensor, a first classificationvoltage within a classification voltage range defined by a lowerclassification voltage limit and upper classification voltage limit;output, via the at least one current source and responsive to thedetected first classification voltage, a first current flow greater thana default classification value limit; detect, via the voltage sensor, avoltage outside of the classification voltage range; subsequent to thedetected voltage outside of the classification voltage range, detect,via the voltage sensor, a second classification voltage within theclassification voltage range; and output, via the at least one currentsource and responsive to the detected second classification voltage, asecond current flow greater than a default classification value limit,the second current flow exhibiting a value responsive to the detectedvoltage outside of the classification voltage range.

In one embodiment the at least one current source comprises a variablecurrent source. In another embodiment the control circuitry is furtheroperable to: output subsequent to the output second current flow, viathe at least one current source and responsive to the secondclassification voltage, a third current flow exhibiting a value lessthan a default classification value limit, and a fourth current flowsubsequent to the third current flow, the fourth current flow exhibitinga value exceeding the default classification value limit. In one furtherembodiment the control circuitry is further operable to outputsubsequent to the output fourth current flow, via the at least onecurrent source, and responsive to the second classification voltage, afifth current flow exhibiting a value exceeding the defaultclassification value limit and a value different than the output fourthcurrent flow.

Independently the invention provides for a method of classification ofpower requirements in a power over Ethernet system, the methodcomprising: providing a first classification voltage within aclassification voltage range defined by a lower classification voltagelimit and upper classification voltage limit; measuring a first currentflow responsive to the provided first classification voltage; subsequentto the provided first classification voltage, providing a voltageoutside of the classification voltage range; subsequent to the providedvoltage outside of the classification voltage range, providing a secondclassification voltage within the classification voltage range;measuring a second current flow responsive to the provided secondclassification voltage; determining a classification responsive to themeasured first current flow and the measured second current flow; andallocating power responsive to said determined classification.

Additional features and advantages of the invention will become apparentfrom the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same maybe carried into effect, reference will now be made, purely by way ofexample, to the accompanying drawings in which like numerals designatecorresponding elements or sections throughout.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice. In the accompanying drawings:

FIG. 1A is a high level schematic diagram of a PoE system comprising aPSE according to the “af” standard and a PD according to the “af”standard according to the prior art;

FIG. 1B is a high level schematic diagram of a PoE system comprising aPSE according to the proposed “at” standard and a PD according to the“af” standard in accordance with a principle of the current invention;

FIG. 1C is a high level schematic diagram of a PoE system comprising aPSE according to the “af” standard and a PD according to the proposed“at” standard in accordance with a principal of the current invention;

FIG. 1D is a high level schematic diagram of a PoE system comprising aPSE according to the proposed “at” standard and a PD according to theproposed “at” standard in accordance with a principle of the currentinvention;

FIG. 2A is a chart of the voltage output of the PSE of FIG. 1Aexhibiting detection, classification and powering of the PD of FIG. 1Ain accordance with the prior art;

FIG. 2B is a chart of the current draw of the PD from the PSE of FIG. 1Aduring classification and initial powering, as sensed at the PSE, inaccordance with the prior art;

FIG. 3A is a chart of the voltage output of the PSE of FIG. 1Bexhibiting detection, classification and powering of the PD of FIG. 1Bin accordance with a principle of the current invention;

FIG. 3B is a chart of the current draw of the PD from the PSE of FIG. 1Bduring classification and initial powering by the PSE, as sensed at thePSE, in accordance with a principle of the current invention;

FIG. 4A is a chart of the voltage output of the PSE of FIG. 1Cexhibiting detection, classification and powering of the PD of FIG. 1Cin accordance with a principle of the current invention;

FIG. 4B is a chart of the current draw of the PD of FIG. 1C duringclassification and initial powering by the PSE, as sensed at the PSE, inaccordance with a principle of the current invention;

FIG. 5A is a chart of the voltage output of the PSE of FIG. 1Dexhibiting detection, classification and powering of the PD of FIG. 1Din accordance with a principle of the current invention;

FIG. 5B is a chart of the current draw of the PD of FIG. 1D duringclassification and initial powering by the PSE, as sensed by the PSE, inaccordance with a principle of the current invention;

FIG. 6A is a high level flow chart of the operation of the PSE of FIG.1B, 1D to classify the attached detected PD in accordance with aprinciple of the current invention; and

FIG. 6B is a high level flow chart of the operation of the PD of FIG.1C, 1D to respond to classification voltages and determine whetherpowering is by an “at” of “af” PSE in accordance with a principle of thecurrent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present embodiments enable a classification scheme exhibiting aplurality of classification cycles within the classification voltagerange, with the PSE voltage being removed from the classificationvoltage range between cycles. Preferably, the PD provides a currentsignature prior to the end of the plurality of cycles by exhibiting afirst current output associated with a first class and a second currentoutput associated with a second class. Further preferably the currentsignature is preceded by a current level not associated with aclassification current. Preferably the first and second classes arenumerically adjacent classes. Further preferably the first and secondclasses are consecutively output with no substantial intervening time.Preferably the PSE outputs a voltage signature indicative that it is an“at” PSE, the output voltage signature comprising lowering the outputvoltage at the end of the plurality of cycles to be less than theclassification voltage range.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is applicable to other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

FIG. 1A is a high level schematic diagram of a PoE system according tothe prior art, comprising a PSE 10 according to the “af” standard, a PD20 according to the “af” standard, a power supply 30 and communicationcabling 25. PSE 10 comprises a control circuitry 40, a detectionfunctionality 50, a classification functionality 60, an electronicallycontrolled switch 70 and a sense resistor 80. PD 20 comprises a controlcircuitry 100, a voltage sensor 90, a controlled current source 110, aload 120 and an associated an input capacitor 130, and an electronicallycontrolled switch 140. A first output of power supply 30 is connectedthrough PSE 10 to a first end of a first lead of communication cabling25. The return of power supply 30 is connected to a first end ofelectronically controlled switch 70 of PSE 10. Control circuitry 40 isin communication with detection functionality 50, classificationfunctionality 60 and the control input of electronically controlledswitch 70. The second end of electronically controlled switch 70 isconnected to a first end of sense resistor 80 and a second end of senseresistor 80 is connected to a first end of a second lead ofcommunication cabling 25. Classification functionality 60 is connectedacross sense resistor 80 thus enabling measurement of current flowthrough sense resistor 80 by measuring the voltage drop across senseresistor 80.

The second end of the first lead of communication cabling 25 isconnected at PD 20 to a first end of voltage sensor 90, a first end ofload 120, a first end of input capacitor 130 and to a first end ofcontrolled current source 110. The second end of the second lead ofcommunication cabling 25 is connected to the second end of voltagesensor 90, the second end of controlled current source 110 and to afirst end of electronically controlled switch 140. The second end ofelectronically controlled switch 140 is connected to the second end ofload 120 and to the second end of input capacitor 130. The output ofvoltage sensor 90 is connected to an input of control circuitry 100 andthe control inputs of controlled current source 110 and electronicallycontrolled switch 140 are connected to respective outputs of controlcircuitry 100.

In operation control circuitry 40 operates detection functionality 50 todetect PD 20 via communication cabling 25. Control circuitry 40 furtheroperates classification functionality 60 to classify, in cooperationwith current source 110, the detected PD 20 as to power requirements.Classification functionality 60 measures the current flow through senseresistor 80 during the classification phase responsive to controlledcurrent source 110 thereby identifying the power requirements of PD 20as a function of the measured current flow. Responsive to detection andclassification, control circuitry 40 operates electronically controlledswitch 70 to connect power supply 30 so as to supply power viacommunication cabling 25 to identified and classified PD 20.

FIG. 1B is a high level schematic diagram of a PoE system in accordancewith a principle of the current invention comprising a PSE 150 accordingto the proposed “at” standard, a PD 20 according to the “af” standard, apower supply 30 and a communication cabling 25. PSE 150 comprises acontrol circuitry 160, a detection functionality 50, a classificationfunctionality 170, an electronically controlled switch 70 and a senseresistor 80. PD 20 comprises a control circuitry 100, a voltage sensor90, a controlled current source 110, a load 120 and an associated inputcapacitor 130, and an electronically controlled switch 140. A firstoutput of power supply 30 is connected through PSE 150 to a first end ofa first lead of communication cabling 25. The return of power supply 30is connected to a first end of electronically controlled switch 70 ofPSE 150. Control circuitry 160 is in communication with detectionfunctionality 50, classification functionality 170 and the control inputof electronically controlled switch 70. The second end of electronicallycontrolled switch 70 is connected to a first end of sense resistor 80and a second end of sense resistor 80 is connected to a first end of asecond lead of communication cabling 25. Classification functionality170 is connected across sense resistor 80 thus enabling measurement ofcurrent flow through sense resistor 80 by measuring the voltage dropacross sense resistor 80.

The second end of the first lead of communication cabling 25 isconnected at PD 20 to a first end of voltage sensor 90, a first end ofload 120, a first end of input capacitor 130 and to a first end ofcontrolled current source 110. The second end of the second lead ofcommunication cabling 25 is connected to the second end of voltagesensor 90, the second end of controlled current source 110 and to afirst end of electronically controlled switch 140. The second end ofelectronically controlled switch 140 is connected to the second end ofload 120 and to the second end of input capacitor 130. The output ofvoltage sensor 90 is connected to an input of control circuitry 100 andthe control inputs of controlled current source 110 and electronicallycontrolled switch 140 are connected to respective outputs of controlcircuitry 100.

In operation control circuitry 160 operates detection functionality 50to detect PD 20 via communication cabling 25. Control circuitry 160further operates classification functionality 170 to classify, incooperation with controlled current source 110, the detected PD 20 as topower requirements. Classification functionality 170 is furtheroperative, as will be described further hereinto below, to detect thatPD 20 is of the low power “af” variety and not a high power “at” device.Classification functionality 170 measures the current flow through senseresistor 80 during the classification phase responsive to controlledcurrent source 110 thereby identifying the power requirements of PD 20as a function of the measured current flow. Responsive to detection andclassification, control circuitry 160 operates electronically controlledswitch 70 to connect power supply 30 so as to supply power viacommunication cabling 25 to identified and classified PD 20.

FIG. 1C is a high level schematic diagram of a PoE system in accordancewith a principle of the current invention comprising a PSE 10 accordingto the “af” standard, a PD 200 according to the proposed “at” standard,a power supply 30 and communication cabling 25. PSE 10 comprises acontrol circuitry 40, a detection functionality 50, a classificationfunctionality 60, an electronically controlled switch 70 and a senseresistor 80. PD 200 comprises a control circuitry 230, a voltage sensor90, a first controlled current source 210, a second controlled currentsource 220, a load 240 and an associated input capacitor 130, anelectronically controlled switch 140 and an indicator 250. A firstoutput of power supply 30 is connected through PSE 10 to a first end ofa first lead of communication cabling 25. The return of power supply 30is connected to a first end of electronically controlled switch 70 ofPSE 10. Control circuitry 40 is in communication with detectionfunctionality 50, classification functionality 60 and the control inputof electronically controlled switch 70. The second end of electronicallycontrolled switch 70 is connected to a first end of sense resistor 80and a second end of sense resistor 80 is connected to a first end of asecond lead of communication cabling 25. Classification functionality 60is connected across sense resistor 80 thus enabling measurement ofcurrent flow through sense resistor 80 by measuring the voltage dropacross sense resistor 80.

The second end of the first lead of communication cabling 25 isconnected at PD 200 to a first end of voltage sensor 90, a first end offirst controlled current source 210, a first end of second controlledcurrent source 220, a first end of load 240 and to a first end of inputcapacitor 130. The second end of the second lead of communicationcabling 25 is connected to the second end a voltage sensor 90, a secondend of first controlled current source 210, a second end of secondcontrolled current source 220 and to a first end of electronicallycontrolled switch 140. The second end of electronically controlledswitch 140 is connected to the second end of load 240, the second end ofinput capacitor 130 and the first end of indicator 250. The output ofvoltage sensor 90 is connected to an input of control circuitry 230 andthe control inputs of first controlled current source 210, secondcontrolled current source 220 and electronically controlled switch 140are connected to respective outputs of control circuitry 230. The secondend of indicator 250 is connected to an output of control circuitry 230.PD 200 is illustrated as comprising first controlled current source 210and second controlled current source 220, however this is not meant tobe limiting in any way. PD 200 may comprise a single controlled variablecurrent source operable to output a plurality of current levelsresponsive to control circuitry 230, or 3 or more controlled currentsources each responsive to control circuitry 230, without exceeding thescope of the invention.

In operation, control circuitry 40 operates detection functionality 50to detect PD 200 via communication cabling 25. Control circuitry 40further operates classification functionality 60 to classify, incooperation with first controlled current source 210, the detected PD200 as to power requirements. Classification functionality 60 measuresthe current flow through sense resistor 80 during the classificationphase responsive to first controlled current source 210 therebyidentifying the power requirements of PD 200 as a function of themeasured current flow. It is to be noted that classificationfunctionality 60 is unable to identify PD 200 as a high power “at”device. Responsive to detection and classification, control circuitry 40operates electronically controlled switch 70 to connect power supply 30to supply power via communication cabling 25 to identified andclassified PD 200.

Control circuitry 230 is operable, as will be described further hereintobelow, to detect that PSE 10 is a low power “af” PSE, and in responseoperate indicator 250 to notify a user of the limited poweringcapabilities. In one embodiment control circuitry 230 closeselectronically controlled switch 140 to power load 240, and in anotherembodiment control circuitry 230 does not power load 240 and indicator250 is operational to indicate that the failure of load 240 to operateis as a result of a low power “af” source.

FIG. 1D is a high level schematic diagram of a PoE system in accordancewith a principle of the current invention comprising a PSE 150 accordingto the proposed “at” standard, a PD 200 according to the proposed “at”standard, a power supply 30 and a communication cabling 25. PSE 150comprises a control circuitry 160, a detection functionality 50, aclassification functionality 170, an electronically controlled switch 70and a sense resistor 80. PD 200 comprises a control circuitry 230, avoltage sensor 90, a first controlled current source 210, a secondcontrolled current source 220, a load 240 and an associated inputcapacitor 130, an electronically controlled switch 140 and an indicator250. A first output of power supply 30 is connected through PSE 150 to afirst end of a first lead of communication cabling 25. The return ofpower supply 30 is connected to a first end of electronically controlledswitch 70 of PSE 150. Control circuitry 160 is in communication withdetection functionality 50, classification functionality 170 and thecontrol input of electronically controlled switch 70. The second end ofelectronically controlled switch 70 is connected to a first end of senseresistor 80 and a second end of sense resistor 80 is connected to afirst end of a second lead of communication cabling 25. Classificationfunctionality 170 is connected across sense resistor 80 thus enablingmeasurement of current flow through sense resistor 80 by measuring thevoltage drop across sense resistor 80.

The second end of the first lead of communication cabling 25 isconnected at PD 200 to a first end of voltage sensor 90, a first end offirst controlled current source 210, a first end of second controlledcurrent source 220, a first end of load 240 and to a first end of inputcapacitor 130. The second end of the second lead of communicationcabling 25 is connected to the second end of voltage sensor 90, a secondend of first controlled current source 210, a second end of secondcontrolled current source 220 and to a first end of electronicallycontrolled switch 140. The second end of electronically controlledswitch 140 is connected to the second end of load 240, the second end ofinput capacitor 130 and the first end of indicator 250. The output ofvoltage sensor 90 is connected to an input of control circuitry 230 andthe control inputs of first controlled current source 210, secondcontrolled current source 220 and electronically controlled switch 140are connected to respective outputs of control circuitry 230. The secondend of indicator 250 is connected to an output of control circuitry 230.PD 200 is illustrated as comprising first controlled current source 210and second controlled current source 220, however this is not meant tobe limiting in any way. PD 200 may comprise a single controlled variablecurrent source operable to output a plurality of current levelsresponsive to control circuitry 230, or 3 or more controlled currentsources responsive to control circuitry 230, without exceeding the scopeof the invention.

In operation, control circuitry 160 operates detection functionality 50to detect PD 200 via communication cabling 25. Control circuitry 160further operates classification functionality 170 to classify, incooperation with first controlled current source 210 and secondcontrolled current source 220, the detected PD 200 as to powerrequirements. Classification functionality 170 measures the current flowthrough sense resistor 80 during the classification phase responsive tofirst controlled current source 210 and second controlled current source220, as will be described further hereinto below, thereby identifyingthe power requirements of PD 200 as a function of the measured currentflows. It is to be noted that classification functionality 170 is ableto identify PD 200 as a high power “at” device. Responsive to detectionand classification, control circuitry 160 operates electronicallycontrolled switch 70 to connect power supply 30 to supply power viacommunication cabling 25 to identified and classified PD 200.

Control circuitry 230 is operable, as will be described further hereintobelow, to detect that PSE 160 is a high power “at” compatible PSE, andthus in response does not operate indicator 250. Control circuitry 230,responsive to a sensed operating voltage, closes electronicallycontrolled switch 140 to supply power to load 240.

FIG. 2A is a chart of the voltage output of PSE 10 exhibiting detection,classification and powering by PSE 10 of PD 20 as depicted in FIG. 1A,in accordance with the prior art, in which the x-axis represents timeand the y-axis represents voltage at the output of PSE 10. A detectionwaveform 300 is presented by PSE 10 representative of detection andexhibits a plurality of voltage levels operable to detect a valid PD 20over communication cabling 25. Subsequent to detection waveform 300, andresponsive to a successful detection by detection functionality 50 incooperation with detection waveform 300, a classification waveform 310is presented by PSE 10. Classification waveform 310 exhibits a voltagelevel at the output of PSE 10 within a classification voltage range 312defined between a lower classification voltage limit 315, illustrated as15.5 volts in accordance with the “af” standard, and an upperclassification voltage limit 317, illustrated as 20.5 volts inaccordance with the “af” standard, and is operable to classify thedetected PD 20 over communication cabling 25. Classification waveform310 is representative of a classification cycle, and is held withinclassification voltage range 312 for a period of time sufficient forcontrol circuitry 100 to detect the classification voltage via voltagesensor 90, enable controlled current source 110 to supply aclassification current responsive thereto and for classificationfunctionality 60 to measurably detect the classification current. Such atime period is denoted hereinafter as a classification cycle time. Attime T₁, PSE 10, having detected and classified PD 20, is operable toincrease the output voltage to an operating voltage nominally alongcurve 320 which is detected by PD 20. PD 20, and in particular controlcircuitry 100, responsive to the detected increased output voltage assensed by voltage sensor 90, nominally around 35 V, is operative toclose electronically controlled switch 140 thereby connecting load 120exhibiting input capacitor 130 across power supply 30. Numerous possibleactual waveforms may occur, of which waveform 330 and waveform 340 aredepicted. Waveform 340 exhibits a voltage decline after point T₁,representative of PSE 10 completing the classification function andpreparing to close electronically controlled switch 70. Inflection point345 is representative of the closing of the electronically controlledswitch 70. The voltage at the output of PSE 10 then begins to rise untilit merges with nominal waveform 320.

Waveform 330 is representative of PSE 10 closing electronicallycontrolled switch 70 after completion of the classification cycle.Inflection point 335 is representative of the closing of electronicallycontrolled switch 140, with a resulting decline in voltage at the outputof PSE 10 due to the appearance of input capacitor 130 across the outputof PSE 10, which acts as a virtual short circuit. Inflection point 350represents a minimum voltage point, after which input capacitor 130 issufficiently charged to allow the output of PSE 10 to rise. It is to beparticularly noted that inflection point 350 is within classificationvoltage range 312, and that inflection point 345 is outside ofclassification voltage range 312, and particularly below classificationvoltage range 312.

FIG. 2B is a chart of the current draw of PD 20 during classificationand initial powering by PSE 10 of FIG. 1A in accordance with the priorart, in which the x-axis represents time and the y-axis representscurrent through PSE 10 as detected by current sense resistor 80.Responsive to classification waveform 310 of FIG. 2A sensed by voltagesensor 90, control circuitry 100 operates controlled current source 110to output one of 4 potential classes described in the above mentioned“af” standard. Each of the classes is represented by differently filledarea ending at point T₁. Class 0, equivalent to a default classificationvalue, is represented by current under a default classification valuelimit 365 at area 360. Default classification value limit 365 isdepicted as 5 mA in according with the “af” standard, and defaultclassification value limit 365 is representative of a PD not exhibitinga classification functionality such as controlled current source 110.Classes 0, 1, 2, 3 and currently unused class 4, are represented bydifferent current values denoted respectively area 360, area 370, area380, area 390 and area 400 as illustrated in FIG. 2B each ending at timeT₁, coincident with, and responsive to, the end of classificationwaveform 310. Sharply rising current 410 represents the closing ofelectronically controlled switch 140 by control circuitry 100 responsiveto the sensed operating voltage generated after point T₁. As describedabove in relation to FIG. 2A, the sharply rising current representativeof input capacitor 130 being placed across PSE 10, may result in areduced output voltage appearing at PSE 10.

FIG. 3A is a chart of the voltage output of PSE 150 exhibitingdetection, classification and powering of PD 20 as depicted in FIG. 1B,in accordance with a principle of the current invention, in which thex-axis represents time and the y-axis represents voltage at the outputof PSE 150. A detection waveform 300 is presented by PSE 10representative of detection and exhibits a plurality of voltage levelsoperable to detect a valid PD 20 over communication cabling 25.Subsequent to detection waveform 300, and responsive to a successfuldetection by detection functionality 50 in cooperation with detectionwaveform 300, a first classification waveform 450 is presented by PSE150, exhibiting a voltage level at the output of PSE 150 within aclassification voltage range 312 defined between a lower classificationvoltage limit 315, illustrated as 15.5 volts in accordance with the “af”standard, and an upper classification voltage limit 317, illustrated as20.5 volts in accordance with the “af” standard, operable to classifythe detected PD 20 over communication cabling 25. Waveform 450 isrepresentative of a first classification cycle, and is held withinclassification voltage range 312 for a period of time sufficient forcontrol circuitry 100 to detect the classification voltage, enablecontrolled current source 110 to supply the classification current andfor classification functionality 170 to measurably detect theclassification current, i.e. for a classification cycle time.

Following the completion of the classification cycle time represented byfirst classification waveform 450, classification indexing waveform 460is presented, in which the voltage output of PSE 150 is outside ofclassification voltage range 312. In one embodiment the voltage is aboveclassification voltage range 312, and in another embodiment, asillustrated, the voltage exhibited by classification indexing waveform460 is below classification voltage range 312. As will be explainedfurther hereinto below in relation to FIGS. 5A and 5B, theclassification indexing waveform 460 is maintained for a classificationindexing time sufficient to ensure that voltage at the output hasstabilized and been sensed by a control circuitry of an “at” PD, ifconnected.

Subsequent to the presentation of the classification index waveform 460,second classification waveform 470 is presented by PSE 150, exhibiting avoltage level at the output of PSE 150 within classification voltagerange 312. Second classification waveform 470 is representative of asecond classification cycle, and is held within classification voltagerange 312 for a period of time sufficient for control circuitry 100 todetect the voltage, and if so configured enable controlled currentsource 110 to supply the classification current, and for classificationfunctionality 170 to measurably detect the classification current, i.e.for a classification cycle time. It is to be understood that PD 20 isnot designed to recognize classification indexing waveform 460, nor isit necessarily configured to respond to second classification waveform470 with an appropriate classification current. Subsequent to secondclassification waveform 470, preferably voltage signature waveform 480is presented by PSE 150 starting at time T₀. Voltage signature waveform480, as will be described further hereinto below in relation to FIGS.5A-6B, is operable to confirm to the attached PD that secondclassification waveform 470 is as a result of an “at” PSE, such as PSE150, and is not as a result of noise or a voltage drop due to a suddencurrent draw as described above in relation to FIG. 2A. Voltagesignature waveform 480 exhibits a voltage below that of classificationvoltage range 312 for a sufficient time period to stabilize and bedetected by control circuitry 230.

At time T₁, PSE 150, having detected and classified PD 20, is operableto increase the output voltage to an operating voltage nominally alongcurve 320 which is detected by PD 20. PD 20, and in particular controlcircuitry 100, responsive to the detected increased output voltageresponsive to the detected increased output voltage as sensed by voltagesensor 90, nominally around 35 V, is operative to close electronicallycontrolled switch 140 thereby connecting load 120 exhibiting inputcapacitor 130 across power supply 30. Numerous possible actual waveformsmay occur, of which waveform 330 and waveform 340, as described above inrelation to FIG. 2A are depicted.

FIG. 3B is a chart of the current draw of PD 20 during classificationand initial powering by PSE 150 of FIG. 1B in accordance with aprinciple of the current invention, in which the x-axis represents timeand the y-axis represents current through PSE 150 as detected by currentsense resistor 80. Responsive to first classification waveform 450 ofFIG. 3A sensed by voltage sensor 90, control circuitry 100 operatescontrolled current source 110 to output one of 4 potential classesdescribed in the above mentioned “af” standard. Each of the classes isrepresented by differently filled area ending with the end of firstclassification waveform 450. Class 0, equivalent to a defaultclassification value, is represented by current under a defaultclassification value limit 365 at area 360. Default classification valuelimit 365 is depicted as 5 mA in according with the “af” standard, anddefault classification value limit 365 is representative of a PD notexhibiting a classification current source. Class 0 is thusrepresentative of PD 20 not exhibiting controlled current source 110.Classes 1, 2, 3 and currently unused class 4, are represented bydifferent current values denoted respectively area 370, area 380, area390 and area 400 as illustrated in FIG. 3B.

Contemporaneously with classification indexing waveform 460, andresponsive thereto, a valid classification current is not defined and isillustrated as current level range 500. It is to be understood that thecurrent level may be any value, as an “af” PD, such as PD 20 does nothave a defined response to classification indexing waveform 460. In oneembodiment PD 20 maintains the classification current, and in anotherembodiment PD 20 turns off the classification current.

Responsive to second classification waveform 470 of FIG. 3A, in oneembodiment as illustrated, control circuitry 100 operates controlledcurrent source 110 to output one of 4 potential classes described in theabove mentioned “af” standard. Each of the classes is represented bydifferently filled area ending at point T₀ corresponding and responsiveto the end of second classification waveform 470. Classes 0, 1, 2, 3 andcurrently unused class 4, are represented by different current valuesdenoted respectively area 360, area 370, area 380, area 390 and area400. It is to be understood that there is no requirement under the “af”standard for PD 20 to respond to second classification waveform 470 witha valid classification current, and in another embodiment noclassification current is drawn during second classification waveform470.

Sharply rising current 410 represents the closing of electronicallycontrolled switch 140 by control circuitry 100 responsive to the sensedoperating voltage generated after point T₁. As described above inrelation to FIG. 2A, the sharply rising current representative of inputcapacitor 130 being placed across PSE 150, may result in a reducedoutput voltage appearing at PSE 150.

FIG. 4A is a chart of the voltage output of PSE 10 of FIG. 1C exhibitingdetection, classification and powering of PD 200 of FIG. 1C inaccordance with a principle of the current invention, in which thex-axis represents time and the y-axis represents voltage at the outputof PSE 10. A detection waveform 300 is presented by PSE 10representative of detection and exhibits a plurality of voltage levelsoperable to detect a valid PD 200 over communication cabling 25.Subsequent to detection waveform 300, and responsive to a successfuldetection by detection functionality 50 in cooperation with detectionwaveform 300, a classification waveform 310 is presented by PSE 10.Classification waveform 310 exhibits a voltage level at the output ofPSE 10 within a classification voltage range 312 defined between a lowerclassification voltage limit 315, illustrated as 15.5 volts inaccordance with the “af” standard, and an upper classification voltagelimit 317, illustrated as 20.5 volts in accordance with the “af”standard, and is operable to classify the detected PD 200 overcommunication cabling 25. Classification waveform 310 is representativeof a classification cycle, and is held within classification voltagerange 312 for a period of classification cycle time sufficient forcontrol circuitry 230 to detect the classification voltage, enable firstcontrolled current source 210 to supply the classification current andfor classification functionality 60 to measurably detect theclassification current. Classification waveform 310 ends at time T₁. Attime T₁, PSE 10, having detected and classified PD 200, is operable toincrease the output voltage to an operating voltage nominally alongcurve 320 which is detected by PD 200. PD 200, and in particular controlcircuitry 230, responsive to the detected increased output voltage assensed by voltage sensor 90, nominally around 35 V, is operative toclose electronically controlled switch 140 thereby connecting load 240exhibiting input capacitor 130 across power supply 30. Numerous possibleactual waveforms may occur, of which waveform 330 and waveform 340,described above in relation to FIG. 2A are depicted. In particular it isto be noted that waveform 330 exhibits an inflection point withinclassification voltage range 312, and PD 200 is operable in accordancewith a principle of the invention, as will be described further hereintobelow, to distinguish that PSE 10 is not a high power “at” PSE.

FIG. 4B is a chart of the current draw of PD 200 during classificationand initial powering by PSE 10 of FIG. 1C in accordance with a principleof the invention, in which the x-axis represents time and the y-axisrepresents current through PSE 10 as detected by current sense resistor80 and measured by classification functionality 60. Responsive toclassification waveform 310 of FIG. 2A sensed by voltage sensor 90,control 230 operates first controlled current source 210 to output oneof 4 potential classes described in the above mentioned “af” standard.Each of the classes is represented by differently filled area ending atpoint T₁. Class 0 is not presented as an “at” PD is designed to respondwith a classification value in excess of a default classification valuelimit 365. Default classification value limit 365 is depicted as 5 mA inaccording with the “af” standard. Classes 1, 2, 3 and currently unusedclass 4, are represented by different current values denotedrespectively area 370, area 380, area 390 and area 400 each ending attime T₁. Sharply rising current 410 represents the closing ofelectronically controlled switch 140 by control circuitry 230 responsiveto the sensed operating voltage generated after point T₁. As describedabove in relation to FIG. 2A, the sharply rising current representativeof input capacitor 130 being placed across PSE 10, may result in areduced output voltage appearing at PSE 10.

FIG. 5A is a chart of the voltage output of PSE 150 exhibitingdetection, classification and powering of PD 200 of FIG. 1D inaccordance with a principle of the current invention, in which thex-axis represents time and the y-axis represents voltage at the outputof PSE 150. A detection waveform 300 is presented by PSE 150representative of detection and exhibits a plurality of voltage levelsoperable to detect a valid PD 200 over communication cabling 25.Subsequent to detection waveform 300, and responsive to a successfuldetection by detection functionality 50 in cooperation with detectionwaveform 300, a first classification waveform 450 is presented by PSE150, exhibiting a voltage level at the output of PSE 150 within aclassification voltage range 312 defined between a lower classificationvoltage limit 315, illustrated as 15.5 volts in accordance with the “af”standard, and an upper classification voltage limit 317, illustrated as20.5 volts in accordance with the “af” standard, operable to classifythe detected PD 200 over communication cabling 25. Waveform 450 isrepresentative of a first classification cycle, and is held withinclassification voltage range 312 for a period of time sufficient forcontrol circuitry 230 to detect the classification voltage, enable firstcontrolled current source 210 to supply the classification current andfor classification functionality 170 to measurably detect theclassification current, i.e. for a classification cycle time.

Following the completion of the classification cycle time represented byfirst classification waveform 450, classification indexing waveform 460is presented, in which the voltage output of PSE 150 is outside ofclassification voltage range 312. In one embodiment the voltage is aboveclassification voltage range 312, and in another embodiment, asillustrated, the voltage exhibited by classification indexing waveform460 is below classification voltage range 312. Classification indexingwaveform 460 is maintained for a classification indexing time sufficientto ensure that voltage at the output has stabilized and been sensed bycontrol circuitry 230. Control circuitry 230 is operative to index theclassification output to enable second controlled current source 220 inthe event that a second classification voltage waveform is detected.

Subsequent to the presentation of the classification index waveform 460,second classification waveform 470 is presented by PSE 150, exhibiting avoltage level at the output of PSE 150 within classification voltagerange 312. Second classification waveform 470 is representative of asecond classification cycle, and is held within classification voltagerange 312 for a period of time sufficient for control circuitry 230 todetect the voltage, and as described above to supply a classificationcurrent from second controlled current source 220, and forclassification functionality 170 to measurably detect the classificationcurrent, i.e. for a classification cycle time. Second classificationwaveform 470 ends at time T₀.

In an optional embodiment, control 230 is further operable to output acurrent signature, as will be described further hereinto below inrelation to FIG. 5B, confirming to PSE 150 that the secondclassification current is a consequence of second controlled currentsource 220 and not a result of noise or an “af” PD exhibiting a secondundefined current responsive to classification indexing waveform 460 andsecond classification waveform 470.

Subsequent to second classification waveform 470, preferably voltagesignature waveform 480 is presented by PSE 150 starting at time T₀.Voltage signature waveform 480, is operable to confirm to PD 200 thatsecond classification waveform 470 is as a result of an “at” PSE, suchas PSE 150, and is not as a result of noise or a voltage drop due to asudden current draw as described above in relation to FIG. 2A. Voltagesignature waveform 480 exhibits a voltage below that of classificationvoltage range 312 for a sufficient time period to stabilize and bedetected by control circuitry 230.

At time T₁, PSE 150, having detected and classified PD 200, is operableto increase the output voltage to an operating voltage nominally alongcurve 320 which is detected by PD 200. PD 200, and in particular controlcircuitry 230, responsive to the detected increased output voltage assensed by voltage sensor 90, nominally around 35 V, is operative toclose electronically controlled switch 140 thereby connecting load 240exhibiting input capacitor 130 across power supply 30. Numerous possibleactual waveforms may occur, of which waveform 330 and waveform 340, asdescribed above in relation to FIG. 2A are depicted

FIG. 5B is a chart of the current draw of PD 200 during classificationand initial powering by PSE 150 of FIG. 1D in accordance with aprinciple of the current invention, in which the x-axis represents timeand the y-axis represents current through PSE 150 as detected by currentsense resistor 80. Responsive to first classification waveform 450 ofFIG. 5A sensed by voltage sensor 90, control 230 operates firstcontrolled current source 210 to output one of 4 potential classesdescribed in the above mentioned “af” standard. Each of the classes isrepresented by differently filled area ending responsive to the end offirst classification waveform 450 and exhibits a current above a defaultclassification value limit 365. Each of the respective classificationcurrents are output for a time period 505 approximately contemporaneouswith, and responsive to, first classification waveform 450. Defaultclassification value limit 365 is depicted as 5 mA in according with the“af” standard. Classes 1, 2, 3 and currently unused class 4, arerepresented by different current values denoted respectively area 370,area 380, area 390 and area 400.

Responsive to classification indexing waveform 460 sensed by voltagesensor 90, a draw down current 510, illustrated as a range below class1, is drawn by PD 200 so as to ensure that classification indexingwaveform 460 is stabilized within the desired range. Draw down current510 is illustrated as being below class 1 and above defaultclassification value limit 365, however this is not meant to be limitingin any way. Draw down current 510 may be any value sufficient to ensurestabilization of classification indexing waveform 460. In one embodimentdraw down current 510 is drawn by an additional controlled currentsource (not shown). In another embodiment, in which a variablecontrolled current source is utilized, the variable controlled currentsource is set an appropriate draw down value sufficient to ensurevoltage stabilization and discharge any capacitance to drawn down theoutput voltage of PSE 150 to define classification indexing waveform460.

Responsive to second classification waveform 470 of FIG. 5A, controlcircuitry 230 operates second controlled current source 220 to outputone of 4 potential classes described in the above mentioned “af”standard. Each of the classes is represented by differently filled areaending at point T₀. Classes 1, 2, 3 and currently unused class 4, arerepresented by different current values denoted respectively area 370,area 380, area 390 and area 400 as illustrated in FIG. 3B and are outputfor a time period 515. It is to be understood that there is norequirement that first and second controlled current source 210, 220output the same or different values. Various combinations may beutilized to produce a plurality of classification codes comprising oneor more classification values.

Time period 515 is sufficient to stabilize the current flow from theoutput of second controlled current source 220, and sufficient to enableclassification functionality 170 to measurably obtain the value of thestabilized current flow through sense resistor 80. Preferably,subsequent to time period 515, control circuitry 230 disables secondcurrent source 220 for a time period depicted as period 520. Minimalcurrent flow, if any, occurs during time period 520 which is of asufficient duration to allow for stabilization of the minimal currentflow, and sufficient to enable classification functionality 170 tomeasurably obtain the value of the minimal current flow through senseresistor 80. The minimal current flow of time period 520 is depicted asa range of values less than default classification value limit 365.

Subsequent to time period 520, preferably control circuitry 230 operatessecond controlled current source 220 to output the class output duringtime period 515 for an additional time period 525. Each of the classesis represented by differently filled area, and classes 1, 2, 3 andcurrently unused class 4, are represented by different current valuesdenoted respectively area 370, area 380, area 390 and area 400. Theabove has been described in which the same class is output during period515 and 525 however this is not meant to be limiting in any way. Inanother embodiment the class output during time period 525 is differentfrom the class output during time period 515 without exceeding the scopeof the invention. Time period 525 is sufficient to stabilize the currentflow from the output of second controlled current source 220, andsufficient to enable classification functionality 170 to measurablyobtain the value of the stabilized current flow through sense resistor80.

Subsequent to time period 525, preferably control circuitry 230 operatesone of first and second controlled current sources 220, 230, or in anembodiment in which a variable controlled current source is utilizedcontrol circuitry 230 sent the variable controlled current source, tooutput a class different from the class output during time period 525for an additional time period 530, ending with time T₀. In oneembodiment a class adjacent to the class output in time period 525 isutilized during time period 530, and in another embodiment the classoutput in time period 505 is utilized. Each of the classes isrepresented by differently filled area, with the adjacent classes toclasses 1, 2, 3 and currently unused class 4, represented by the samemarkings as the original classes respectively area 370, area 380, area390 and area 400. The above has been described in which the adjacentclass is output during period 530 however this is not meant to belimiting in any way. Time period 530 is sufficient to stabilize thecurrent flow from the output of second controlled current source 220,and sufficient to enable classification functionality 170 to measurablyobtain the value of the stabilized current flow through sense resistor80. Time period 530 ends at time T₀. Sharply rising current 410represents the closing of electronically controlled switch 140 bycontrol circuitry 100 responsive to the sensed operating voltagegenerated after point T₁. As described above in relation to FIG. 2A, thesharply rising current representative of input capacitor 130 beingplaced across PSE 10, may result in a reduced output voltage appearingat PSE 10.

The above has been described in relation to an embodiment in which thepower over Ethernet controller presents a first classification cycle, aclassification indexing, and a second classification cycle, however thisis not meant to be limiting in any way. Three or more classificationcycles each separated by a classification indexing may be providedwithout exceeding the scope of the invention.

FIG. 6A is a high level flow chart of the operation of PSE 150 of FIG.1B, 1D to classify the attached detected PD 20, 200 respectively, inaccordance with a principle of the current invention. In stage 1000 afirst classification voltage is provided by PSE 150. In stage 1010 acurrent flow responsive to the first classification voltage of stage1000 is measured by classification functionality 170. In stage 1020 aclassification indexing voltage is provided by PSE 150. Theclassification indexing voltage is out of the classification voltagerange defined by a lower classification voltage limit and an upperclassification voltage limit. The classification indexing voltage ispresented for a sufficient time for the voltage to stabilize and for theattached PD to recognize the classification indexing if so configured.

In stage 1030 a second classification indexing voltage is provided byPSE 150. In stage 1040 a current flow responsive to the secondclassification voltage of stage 1030 is measured by classificationfunctionality 170. In stage 1050, PSE 150 optionally supplies a voltagesignature as described in relation to voltage signature 480 of FIG. 5A.

In stage 1060 the first current flow measured in stage 1010, and thesecond current flow measured in stage 1040 are compared. In the eventthat the current flows are substantially equal, in stage 1110 the PD isdetermined to be a low power “af” device, i.e. PD 20 of FIG. 1B. Inresponse to the determination, PSE 150 classifies the power requirementsas a function of the first current flow. In stage 1120, power isallocated to the determined PD 20 responsive to the classification ofstage 1110. In stage 1130, PSE 150 allocates power and powers thedetermined and classified PD 20 with low power in accordance with the“af” standard.

In the event that in stage 1060 the first current flow and secondcurrent flow are not substantially equal, in stage 1070, optionallydetection of a current signature as described in relation to FIG. 5B,and in particular time periods 520 and 525, and optionally time period530, is examined. The operation of stage 1070 is optional in that it isa second check to ensure accurate determination between a low power “af”PD and a high power “at” PD.

In the event that in optional stage 1070 the current signature is notdetected, stage 1110 as described above is performed. In the event thatin stage 1070 the current signature is detected, in stage 1080 the PD isdetermined to be a high power “at” device, such as PD 200 of FIG. 1D. Inresponse to the determination, PSE 150 classifies the power requirementsas a function of a combination of the first current flow measured instage 1010 and of the second current flow measured in stage 1040. Instage 1090, power is allocated to the determined PD 200 responsive tothe classification of stage 1070. In stage 1100, PSE 150 allocates powerand powers the determined and classified PD 200 in accordance with the“at” powering requirements.

Thus, the operation of FIG. 6A determines whether the attached PD is alow power “af” PD such as PD 20 or a high power “at” PD such as PD 200.Furthermore, the operation of FIG. 6A preferably confirms to PD 200 thatit is connected to an “at” PSE.

FIG. 6B is a high level flow chart of the operation of PD 200 of FIG.1C, 1D to respond to classification voltages and determine whetherpowering is by an “at” PSE, such as PSE 150 of FIG. 1D, or an “af” PSE,such as PSE 10 of FIG. 1C, in accordance with a principle of the currentinvention. In stage 2000 control 230 detects a first classificationvoltage output by either PSE 10 or PSE 150. In stage 2010, responsive tothe detected first classification voltage of stage 2000, control 230operates first controlled current source 210 to output a firstclassification current at a predetermined level.

In stage 2020, control circuitry 230 monitors voltage sensor 90 todetect a first classification indexing voltage output by PSE 150 such asclassification indexing waveform 460 of FIG. 5A. In the event thatclassification indexing waveform 460 is detected, in stage 2030 a secondclassification voltage output by PSE 150 is detected by monitoring theoutput of voltage sensor 90. In stage 2040, responsive to the detectedsecond classification voltage of stage 2030, control circuitry 230operates second controlled current source 220 to output a secondclassification current at a predetermined level. In one embodiment firstclassification current output by first controlled current source 210 isof a different value than the second classification current output bysecond controlled current source 220, however this is not meant to belimiting in any way. First classification current output by firstcontrolled current source 210 may be of the same value as the secondclassification current output by second controlled current source 220without exceeding the scope of the invention.

In stage 2050, optionally, second classification current flow output bysecond controlled current source 220 is reduced to a value less than thedefault classification value limit 365. Preferably, the optionalreduction of the current flow value occurs after a sufficient time forthe current flow to have stabilized and be measurably detected bydetection functionality 170. In stage 2060, optionally, secondclassification current flow output by second controlled current source220 is increased to a classification current greater than defaultclassification value limit 365. In one embodiment the current flowoutput of stage 2060 is of the same value as the current flow output ofstage 2040, however this is not meant to be limiting in any way. Thecurrent flow output of stage 2060 may be greater than or less than thevalue of the current flow output of stage 2040, provided that it isgreater than default classification value limit 365, without exceedingthe scope of the invention. Preferably the current flow output of stage2060 represents a valid classification value. The current flow output ofstage 2060 is maintained for a period of time sufficient for the currentflow to stabilize and to be measurably detected and sampled byclassification functionality 170. In stage 2070, optionally, the valueof the current flow output of stage 2060 is changed to a different valuegreater than default classification value limit 365. In one embodimentthe current flow output of stage 2070 represents an adjacent validclassification value to the classification value of stage 2060. Forexample, in the event that the output of stage 2060 was representativeof class 3, the output of stage 2070 representative of class 2. In theevent that the output of stage 2060 is representative of class 1,preferably the output of stage 2070 represents class 4, thusrepresenting adjacency in a circular manner through the active classes.

Stages 2050 through 2070 are optional, as the current signaturerepresents a second confirmation that PD 200 is an “af” PD. Any or allof stages 2050 through 2070 may be optionally implemented withoutexceeding the scope of the invention. In particular stages 2050 and 2060may be implemented without stage 2070 without exceeding the scope of theinvention.

In stage 2080, optionally a voltage signature output by PSE 150, such asvoltage signature waveform 480 of FIG. 5A, is detected by monitoringvoltage sensor 90. Stage 2080 is optional in that it represents afurther confirmation that the PSE is of the “at” high power type. In theevent that the voltage signature is detected, in stage 2090 voltagesensor 90 is monitored until an operating voltage level is detected. Inthe event that an operating voltage is not detected stage 2090 isrepeated. In the event that an operating voltage is detected, in stage2100 control 230 closes electronically controlled switch 140 to powerload 240.

In the event that in stage 2020 the classification indexing voltage wasnot detected, or in the event that in optional stage 2080 the voltagesignature was not detected, in stage 2110 voltage sensor 90 is monitoreduntil an operating voltage level is detected. In the event that anoperating voltage is not detected, stage 2110 is repeated. In the eventthat in stage 2110 an operating voltage is detected, in stage 2120indicator 250 is set to indicate that low power “af” PSE 10 isconnected. In stage 2130 control circuitry 230 closes electronicallycontrolled switch 140 to power load 240 with reduced power.

The above has been described in an embodiment in which an “at” PD, suchas PD 200, powers load 240 with low power from an “af” PSE, such as PSE10. This is not meant to be limiting in any way and in anotherembodiment control circuitry 230 sets indicator 250 to indicate that alow power “af” PSE, such as PSE 10, is connected and stage 2130 is notperformed. In such an embodiment indicator 250 indicates that PD 200 isnot defective, but is instead connected to an improper powering source.

The method of FIG. 6B thus enables PD 200 to identify the poweringsource, be it an “af” PSE, such as PSE 10 of FIG. 1C, or an “at” PSE,such as PSE 150 of FIG. 1D.

Thus, the present embodiments enable a classification scheme exhibitinga plurality of classification cycles within the classification voltagerange, with the PSE voltage being removed from the classificationvoltage range between cycles. Preferably, the PD provides a currentsignature prior to the end of the plurality of cycles by exhibiting afirst current output associated with a first class and a second currentoutput associated with a second class. Further preferably the currentsignature is preceded by a current level not associated with aclassification current. Preferably the first and second classes arenumerically adjacent classes. Further preferably the first and secondclasses are consecutively output with no substantial intervening time.Preferably the PSE outputs a voltage signature indicative that it is an“at” PSE, the output voltage signature comprising lowering the outputvoltage at the end of the plurality of cycles to be less than theclassification voltage range.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meanings as are commonly understood by one of ordinaryskill in the art to which this invention belongs. Although methodssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods aredescribed herein.

All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the patent specification, including definitions, willprevail. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined by the appended claims and includes both combinations andsubcombinations of the various features described hereinabove as well asvariations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot in the prior art.

1. A method of classification of power requirements in a power overEthernet system, said method comprising: providing a firstclassification voltage for a first classification cycle time, saidprovided first classification voltage being within a classificationvoltage range defined by a lower classification voltage limit and upperclassification voltage limit; measuring a first current flow responsiveto said provided first classification voltage; subsequent to said firstclassification cycle time, providing a voltage outside of saidclassification voltage range for a classification indexing time;subsequent to said classification indexing time, providing a secondclassification voltage for a second classification cycle time, saidprovided second classification voltage being within said classificationvoltage range; measuring a second current flow responsive to saidprovided second classification voltage; determining a classificationresponsive to said measured first current flow and said measured secondcurrent flow.
 2. A method according to claim 1, further comprisingallocating power responsive to said determined classification.
 3. Amethod according to claim 1, further comprising: subsequent to saidsecond predetermined classification cycle time, providing a signaturevoltage for a voltage signature time, said signature voltage being belowsaid classification voltage range.
 4. A method according to claim 3,further comprising subsequent to said predetermined voltage signaturetime, providing an operating voltage.
 5. A method according to claim 3,further comprising in the event that said signature voltage is notdetected, identifying a power sourcing equipment associated with saidclassification voltage as a low power source.
 6. A method according toclaim 1, wherein said first current flow and said second current floware of different values.
 7. A method according to claim 6, wherein saiddifferent values of said current flow is responsive to said voltageoutside of said classification voltage range for said classificationindexing time.
 8. A method according to claim 1, further comprisingresponsive to said provided second classification voltage: providingsaid second current flow at a first value for a first time period, saidfirst value exceeding a default classification value limit; subsequentto said first time period, reducing said second current flow to a secondvalue for a second time period, said second value being less than saiddefault classification value limit; and subsequent to said second timeperiod, increasing said second current flow to a third value for a thirdtime period, said third value exceeding said default classificationvalue limit; said second and third values for said respective first,second and third time periods defining a current signature.
 9. A methodaccording to claim 8, further comprising subsequent to said third timeperiod, changing said second current flow to a fourth value for a fourthtime period, said fourth value exceeding said default classificationvalue limit and being different than said third value.
 10. A methodaccording to claim 8, further comprising detecting said currentsignature, and identifying a powered device associated with said currentsignature as a high power device.
 11. A method according to claim 8,wherein said default classification value limit is 5 mA.
 12. A methodaccording to claim 1, wherein said lower classification voltage limit is15.5 volts and said upper classification voltage limit is 20.5 volts.13. A power over Ethernet system comprising: a power sourcing equipment,comprising a classification functionality operable to: provide a firstclassification voltage for a first classification cycle time, saidprovided first classification voltage being within a classificationvoltage range defined by a lower classification voltage limit and upperclassification voltage limit; measure a first current flow responsive tosaid provided first classification voltage; subsequent to said firstclassification cycle time, provide a voltage outside of saidclassification voltage range for a classification indexing time;subsequent to said classification indexing time, provide a secondclassification voltage for a second classification cycle time, saidprovided second classification voltage being within said classificationvoltage range; measure a second current flow responsive to said providedsecond classification voltage; and determine a classification responsiveto said measured first current flow and said measured second currentflow.
 14. A power over Ethernet system according to claim 13, furthercomprising a powered device connected to the power sourcing equipmentover a communication cabling, wherein said power sourcing equipment isfurther operable to allocate a predetermined amount of power to saidpowered device responsive to said determined classification.
 15. A powerover Ethernet system according to claim 14, wherein said power sourcingequipment is operable subsequent to said predetermined voltage signaturetime to provide an operating voltage to said powered device.
 16. A powerover Ethernet system according to claim 14, wherein said powered deviceis operable in the event that said signature voltage is not detected toidentify said power sourcing equipment as a low power source.
 17. Apower over Ethernet system according to claim 14, wherein said powereddevice is operable responsive to said voltage outside of saidclassification voltage range for said classification indexing time toset said second current flow to a different value from said firstcurrent flow.
 18. A power over Ethernet system according to claim 14,wherein said powered device comprises a control circuitry and a currentsource responsive to said control circuitry of said powered device, andwherein said control circuitry of said powered device is operableresponsive to said provided second classification voltage to: providesaid second current flow from said current source at a first value for afirst time period, said first value exceeding a default classificationvalue limit; subsequent to said first time period, reduce said secondcurrent flow from said current source to a second value for a secondtime period, said second value being less than said defaultclassification value limit; and subsequent to said second time period,increase said second current flow from said current source to a thirdvalue for a third time period, said third value exceeding said defaultclassification value limit; said second and third values for saidrespective second and third time periods defining a current signature.19. A power over Ethernet system according to claim 18, wherein saidcontrol circuitry of said powered device is further operable responsiveto said provided second classification voltage to: subsequent to saidthird time period, change said second current flow form said currentsource to a fourth value for a fourth time period, said fourth valueexceeding said default classification value limit and being differentthan said third value.
 20. A power over Ethernet system according toclaim 18, wherein said classification functionality if further operableto: detect said current signature; and identify a powered deviceassociated with said current signature as a high power device.
 21. Apower over Ethernet system according to claim 18, wherein said defaultclassification value limit is 5 mA.
 22. A power over Ethernet systemaccording to claim 13, wherein said classification functionality isfurther operative to: provide a signature voltage for a voltagesignature time subsequent to said second predetermined classificationcycle time, said signature voltage being below said classificationvoltage range.
 23. A power over Ethernet system according to claim 13,wherein said lower classification voltage limit is 15.5 volts and saidupper classification voltage limit is 20.5 volts.
 24. A power overEthernet system comprising: a powered device; a power sourcing equipmentconnected to said powered device over a communication cabling, saidpower sourcing equipment comprising a classification functionality and acurrent sensor and operable to: provide a first classification voltagefor a first classification cycle time, said provided firstclassification voltage being within a classification voltage rangedefined by a lower classification voltage limit and upper classificationvoltage limit; measure, via said current sensor, a first current flowprovided by said powered device responsive to said provided firstclassification voltage; provide, subsequent to said first classificationcycle time, a voltage outside of said classification voltage range for aclassification indexing time; provide, subsequent to said classificationindexing time, a second classification voltage for a secondclassification cycle time, said provided second classification voltagebeing within said classification voltage range; measure, via saidcurrent sensor, a second current flow provided by said powered deviceresponsive to said provided second classification voltage and saidvoltage outside of said classification voltage range; determine aclassification responsive to said measured first current flow and saidmeasured second current flow; and allocate power to said powered deviceresponsive to said determined classification.
 25. A power over Ethernetsystem according to claim 24, wherein said powered device comprises atleast one current source, said first and second current flows beingprovided by said powered device by said at least one current source. 26.A power over Ethernet system according to claim 24, wherein said powereddevice comprises a variable current source, said first and secondcurrent flows being provided by said powered device by said variablecurrent source.
 27. A power over Ethernet system according to claim 24,wherein said powered device comprises a voltage sensor, a controlcircuitry in communication with said voltage sensor, and at least onecurrent source responsive to said control circuitry, said controlcircuitry being operable to: detect, via said voltage sensor, said firstclassification voltage; provide, via said at least one current source,said first current flow; detect, via said voltage sensor, said voltageoutside of said classification voltage range and said subsequent secondclassification voltage; and provide, via said at least one currentsource, said second current flow.
 28. A power over Ethernet systemaccording to claim 27, wherein said at least one current sourcecomprises a variable current source.
 29. A power over Ethernet systemaccording to claim 27, wherein said control circuitry is furtheroperable to provide, via said at least one current source, subsequent tosaid provided second current flow and responsive to said secondclassification voltage, a third current flow exhibiting a value lessthan a default classification value limit, and a fourth current flowsubsequent to said third current flow, said fourth current flowexhibiting a value exceeding said default classification value limit.30. A power over Ethernet system according to claim 29, wherein saidcontrol circuitry is further operable to provide, via said at least onecurrent source, subsequent to said provided fourth current flow andresponsive to said second classification voltage to provide fifthcurrent flow exhibiting a value exceeding said default classificationvalue limit and a value different than said fourth current flow.
 31. Apowered device for a power over Ethernet system comprising: a controlcircuitry; a voltage sensor in communication with said controlcircuitry; and at least one current source responsive to said controlcircuitry, said control circuitry being operative to: detect, via saidvoltage sensor, a first classification voltage within a classificationvoltage range defined by a lower classification voltage limit and upperclassification voltage limit; output, via said at least one currentsource and responsive to said detected first classification voltage, afirst current flow greater than a default classification value limit;detect, via said voltage sensor, a voltage outside of saidclassification voltage range; subsequent to said detected voltageoutside of said classification voltage range, detect, via said voltagesensor, a second classification voltage within said classificationvoltage range; and output, via said at least one current source andresponsive to said detected second classification voltage, a secondcurrent flow greater than a default classification value limit, saidsecond current flow exhibiting a value responsive to said detectedvoltage outside of said classification voltage range.
 32. A powereddevice according to claim 31, wherein said at least one current sourcecomprises a variable current source.
 33. A powered device according toclaim 31, wherein said control circuitry is further operable to: outputsubsequent to said output second current flow, via said at least onecurrent source and responsive to said second classification voltage, athird current flow exhibiting a value less than a default classificationvalue limit, and a fourth current flow subsequent to said third currentflow, said fourth current flow exhibiting a value exceeding said defaultclassification value limit.
 34. A powered device according to claim 33,wherein said control circuitry is further operable to output subsequentto said output fourth current flow, via said at least one currentsource, and responsive to said second classification voltage, a fifthcurrent flow exhibiting a value exceeding said default classificationvalue limit and a value different than said output fourth current flow.35. A method of classification of power requirements in a power overEthernet system, said method comprising: providing a firstclassification voltage within a classification voltage range defined bya lower classification voltage limit and upper classification voltagelimit; measuring a first current flow responsive to said provided firstclassification voltage; subsequent to said provided first classificationvoltage, providing a voltage outside of said classification voltagerange; subsequent to said provided voltage outside of saidclassification voltage range, providing a second classification voltagewithin said classification voltage range; measuring a second currentflow responsive to said provided second classification voltage;determining a classification responsive to said measured first currentflow and said measured second current flow; and allocating powerresponsive to said determined classification.